Signaling system



' Patented Jan. 22, 1924.

v UNITED STATES PATENT OFFICE.

FREDERICK R. LACK, OF PEKIN, CHlNA; AND PAUL B. M 'URI'HY, OF NYACK, NEW YORK, ASSIGNORS TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

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Application filed September To all whom it may concern Be it known thatwe, FREDERICK R. LACK and PAUL B. MURPHY, citizens of the United States, residing at Pekin, China and at N ack, in the county of Rockland, state of ew York, respectivel have invented certain new and useful improvements in Signaling Systems, of which the following is a full, clear, concise, and exact description.

The present invention relates to si aling by controlling the energy of sustaine waves in accordance with signal indications to be sent and in a manner generally known as wave modulation.

In telegraphy by sustained waves, transmitted either over Wires or through space, it

is common to distinguish the signal elements from the space elements of the signal by a change of wave length of the transmitted Wave, or by sending a train of waves for the duration of the signal element and no Waves for a space, or by chopping the transmitted wave at a definite rate as by a buzzer to denote the signal elements sometimes called buzzer modulated telegraphy, or by What is also termed modulatin the wave, that is controlling the amplitude of the transmitted Wave in accordance with a definite low frequency or tone derived from a buzzer or other source without actually chopping the Wave. The distinction between the last two methods is not clear-cut, but a change of adj ustment is sometimes all that is required to change the wave from a chopped wave to a continuous wave the amplitude of which is varied between two finite values at a low frequency rate. For the purposes of the present description and claims the terms modulated wave telegraphy will be used broadl' to denote that the sustained wave is controlled to give it a periodic variation at a tone rate Whether the wave be actually divided into discontinuous Wave trains or not.

Modulated wave telegraphy possesses several advantages among which are the possibility of greater selection since the receiver may be tuned to the tone frequency, greater freedom from disturbances since the car can detect the tone even from noise currents of greater energy, simplification of the receiver circuit over what is required for other types of continuous wave systems, a feature of value particularly in systems having several 7, 1922. Serial a... 588,014.

receiving stations cooperating with a single transmitting station, and still other advantages both in simplex and multiplex systerns.

In application Serial No. 406,584, filed August 28, 1920, by Paul B. Murphy, there is disclosed and claimed a calling system for use in a wave signaling system, the calling arrangement comprising means for sending alternately at a definite rate each of two different tone modulations of the same sustamed wave. A considerable amount of apparatus is required to accomplish this function and since this apparatus has heretofore only been used in calling, it is idle much of the time.

It is an object of the invention to provide for utilizing this ringing or calling apparatus also for modulated wave telegraphy or the like. By virtue of such provision the signaling capacity of the system is increased so that in addition to tele hone and call-signal transmissions, modu ated wave telegraphy can also be carried on, and that b the addition of very simple apparatus s'uc as a key, or a key and a relay or the like, Thus the modulated telegraph transmission may supplement the normal telephone transmission to advantage in a number of ways. For example, if the atmospheric conditions are such as to render telephone transmission difiicult or im ssible, a message may oftentimes be put t rough by means of the modulated telegraph transmission since it is comparatively easy for a skilled operator to distinguish the characteristic tone. The tone oscillator used in the two-tone ringing system referred to is particularly advantageous for telegraphing because of the purity and constancy of the tone produced. For example, such a source is in this important respect far superior to a buzzer, which, at best, gives a much less constant and pure tone and hence one that is more dificult to read thru interference.

Other objects and features will appear from the following detailed description of the particular embodiment of the invention that is diagrammatically illustrated, by way of example, in the accompanying drawing.

This drawin shows a two-Way radio telephone termina equipped with a two-tone ringing or calling arrangement substantially as disclosed in the application referred to above, and provided also with control circuits for utilizing the calling or ringing arran ements for modulated telegraphy in accor ance with the invention.

The radio terminal com rises the transmitting antenna AT an the receiving antenna, which may conveniently be a loop antenna, BL each connected over a suitable path with. the voice fre uency apparatus, which in turn is associa with the hybrid coil H to enable two-way communlcation with ordinary telephone a paratus adapted to be operatively associate with the hy rid coil H. The system is shown arranged so that the radio frequency apparatus maybe located partly at a radio transmitting point and partly at a separated rad1o receiving point, both of which points may be separated from the common sendmgand receiving station at which the speech-frequency terminals of the radio channel are situated, and this common station may also be located at a distance from an ordinary telephone exchange thru which calls for the radio channel may beextended or received. It will be understood that the two-way rad1o terminal of the drawing is arranged for communicating with one or more distant two-way radio terminals which may be simllar to that shown, and that at each such terminal the receiving RL will be arran ed to receive from tide distant terminal ut to be substantially unaffected by waves \sent out from the antenna AT 0t its own station, all

of which is common ractice in the art.

The operators position indicated at OP may be in the telephone exchange and a connection from this point ma be extended over the link line LL to the hy rid coil H at the common sending and receiving station. A. network N is rovided as usual to balance the link line L and associated apparatus. The transmitting branch 3 of the hybrid coil is extended to the voice frequency amplifiers A, and A from which the outlgoing l1ne 0L leads to a radio transmitter R The amplifiers A, and A may be of any suitable type and are shown as comprising the well known electron discharge tube amplifiers. The radio transmitter may be of any suitable .desi n such for example as that shown in U. Patent to Heising 1,442,147, issued January 16, 1923 for modulating a sustained radio frequency wave in accordance with low frequency variations such as speech, ringing, or telegraph tone supplied to it over the line OL.

Associated with the receiving loop RL through suitable tuned circuits. is the detector D, which is preferably arran ed to be supplied from the oscillator O wit a continuous wave differing in fro uency from the received wave by an inaudible fre uency. The output wave of the inaudible di erence frequency produced by the detector D menses which may be conveniently called an intermediate fr uency modulated wave, is amplified by the intermediate frequency am lifier TFA and is passed thru a band filter F to the input side of a detector D The detectors D, and D may each be of the well known electron discharge type, the amplifier IFA may be similar to A, and A, and the band filter may be desi ed in accordance with the disclosure in nited States Patent 1,227,113 issued May 22, 1917 to G. A. Campbell. The oscillator 0 may be of the type shown in U. S. Patent 1,356,763, issued October 26, 1920 to Hartley. The arrangement of the elements in the receivin side of the system is somewhat similar to t at disclosed and described in U. S. Patent 1,361,487 issued December 7, 1920 to Osborne. The detector D, supplies to the incomin line lL the voice-frequency currents or cal ing or tone telegraph frequency currents depending on the character of modulation of the received wave. The amplifiers A, and A, may be similar to A and A, and are provided for am lifying the received signal currents.

or producing the two tones for ringin throu h the system, the oscillator 15 and ampli or 16 are arranged under control of suitable circuits to impress alternately two difierent tones on the amplifier A, for transmission. The oscillating discharge tube 15 is provided with mutually related coils 17 with which a tuning condenser 18 is permanently associated and with which a second tuning condenser 19' is arranged to be associated periodically by the olarized relay 20, when this relay 1S supplied with alternating rin 'ng current from a source indicated at 21. his source may be a standard source of rin 'ng current of 16% cycle frequency, and wfiian energized the relay 20 will cause its armature to vibrate and alternately connect condenser 19 in shunt with condenser 18 and again disconnect it. The frequency of the tone generated by the tube 15 and its associated clrcuits is primaril dependent upon the natural frequency of t e tuned circuit constituted by the condenser 18 and the winding of transformer 17 and is in this manner changed from one definite value to another, both preferably lying within the speech range.

To receive these two tone frequencies, a circuit is provided at the distant station to be communicated with, which circuit may be identical with that shown in the drawing for receivin ringing signals from the distant station. is circuit comprises an amplifier A, the output of which is associated with 1 circuits 24 and 25 arranged to be anti-resonant to the two respective tone frequencies. The rectifiers R and B render the received tone-frequency waves capable of vibrating the armature of a relay 26 in the same way that armature of the relay 20 at the transmitter is vibrated, and a signaling lam 29 is operated under control of this receiving relay.

The system thus far described is substantiall as disclosed inthe application of P. B. lVlhrphy, Serial No. 406,584 and its operation is as follows:

Any suitable telephone circuit may be connected to the h brid coil H by plugging into the jack 2. or example, a local operator may connect her headset or the set of a subscriber with the jack 2, or the operators set or a subscribers line located in the exchan e served by the operator at the position P may be connected through the link LL to the jack 2. The operator at the common transmitting or receiving station in transmitting a call over theradio link in response to a call received from a subscribers line or from an A operator closes the filament starting key FS and the ringing key BK. The switch F S supplies filament heating current from the grounded battery connected thereto to the cathodes of the tubes 15 and 16. The key RK closes an energizing circuit for relay 32 which pulls up its armatures and connects b way of its inner left-hand armature the p ate current source 37 to the plate of the oscillator tube 15, and b way of its right-hand armature connects tli e source 37 to the plate of the amplifier 16. These tubes are thus put into their op erating condition and the tube 15 is caused to generate tone oscillations. The lowermost contact of he BK supplies ound to relays 4 ancl30, which energize. elag 30 in energizin cuts 0d the receiving si e of the calling circuit to prevent its possible actuation due to any unbalance between the transmitting and receiving sides of the system. Relay 4 disconnects the talking circuit 3 from the transmitting side of the radio link, and at its front contacts closes an alternating current circuit from the output side of amplifier 16 so that the waves enerated by the oscillator 15 are supplie to the transmitting side of the radio hnk, the switch S being normally closed. This circuit may be traced from ground, amplifier l6, switch S lower front contact of relay 4, primary winding of repeating coil 5, upper front contact of relay 4 to ground. Relay 32 at its outer left-hand armature closes the circuit including the alternating'source 21 and the polarized relay 20, which causes its armature to vibrate and alternately connect and disconnect the condenser 19 to shift the frequency of the oscillator. During the time that the key BK is depressed these alternate tones are supplied through the transformer 5, amplifiers A, and A repeating coil 6, and outgoing line 0L to the radio transmitter RT, where they modulate the radio carrier wave.

A radio carrier wave modulated by the alternate tone frequencies is received at the distant station to be communicated with, whlch may have an arrangement similar to that of the station shown in the drawing. As stated above the receiving loop BL is preferably arranged in a manner known in the art to receive substantially no radiated energy from the transmitting antenna AT at the same station, and this effect may be increased by the use of radio Waves of different frequencies for the different directions of transmission. Since the distant station, except for these differences, may be similar to t-heone shown, the action of the wave transmitted from the antenna AT and received at the distant station will be clear from consideringthe efiect of a wave transmitted from a distant station and received at the loop FL.

The tone-modulated wave is selectively transmitted by the tuned circuit 8 and has 'its frequency step ed down in the detector D by demodulation with the locally received wave as described in the Osborne Patent No. 1,361,487. The resultant Wave is amplified at IFA and selectively transmitted at BF to the detector D which serves to derive from the intermediate frequency wave waves of the tone frequencies. These are transmitted over theline TL, repeating coil 9, thru the amplifiers A and A -antl the circuit 11 to the input side of amplifier A the relay 30 being normally deenergized. The circuit 24 furnishes a substantially infinite impedance across the coil'38 for currents of one of the tone frequenciesbut substantially zero impedance to the other tone frequency. Similarly the circuit 25 furnishes substantially infinite impedance in shunt of the coil 39 to the other of the two tone frequencies, but a substantially zero impedance to the first tone frequency. The result is that currents of one of the tone frequencies are substantially exclusively im pressed on rectifier R and currents of the other tone frequency are substantially exclusively impresmd on the rectifier R The coils of the polarized relay 26 are therefore alternately impulsed in response to the reception of the alternate tone frequencies and the armature of this relay is vibrated between the two opposite contacts. This armature may be normally biased to close a particular one of its contacts, for example, the upper contact or it may be arranged to remain closed against the con tact to which it was last thrown. In either case the slow-release relay 27 is normally held energized and causes the circuit of relay 28 to remain open. The armature of re lay 26 is so arranged that when it vibrates at the rate of alternation of the two tones in response to the receipt of ringing, the time of closure of its alternate cont-acts is of such short duration that the current thru the relay 27 is reduced to a value below that which is required to hold the relay operated. Relay 27 therefore is caused to release and close the circuit of relay 28 to light the lamp 29. A single impulse of current of the proper frequency to be transmitted to the rectifier R, or R if of sufiicient amplitude to separate the armature of relay 26 from one of its resting contacts, would throw the armature to the other extreme contact but this would not permit relay 27 to deenergize since it is made slow to release. In this manner a high degree of selectivity is provided so that only by impulsin the relay 26 at a definite rate can the relay 27 be released to operate signal 29. The operator at the called station on seeing the lighting of lamp 29 may connect her headset with the jack 2 in order to receive a communication from the distant calling operator.

On releasing the key RK and opening the switch FS the calling operator restores the calling circuits to their normal inactive condition, relay 4 deenergizes to connect the talking circuit 3 with the radio transmitting link, and relay 30 in deenergizing again associates the call-receiving circuits with the circuit 11. Voice currents from the operators set or from the subscriber at the originating end of the system are transmitted to the hybrid coil H and thru the circuit 3 to the repeating coil 5 from which they are transmitted in a manner entirely similar to that described for the calling tone frequencies. At the distant station they are received and detected in a manner entirely similar to that described for the calling tone frequencies and are impressed as waves of speech frequency on the circuit 11 from which they are transmitted thru the h brid coil H to the jack terminal 2 and to wliatever circuit is at the time associated therewith. The speech currents so received will contain some frequencies corresponding with those used in calling, but since these frequencies will not occur in the proper order and at the proper rate for vibrating the armature of relay 26 the signal 29 will not be operated. The circuit for receiving the ringing currents, in bridge of the circuit 11 and extending thru the back contacts of relay 30, is preferably so proportioned as not to shunt the voice currents to a great extent.

Turning now to the circuits which in accordance with the invention have been provided to enable modulated telegraph transmission by means of the tone-modulating circuits above described, these will be seen to comprise the telegraph startin switch TS with its associated relay 33 and the key T or its alternative, the key T and its associated relay 31.

To transmit modulated telegraph signals near,

the operator closes the filament startin switch FS and the telegraph starting switc TS. The switch FS closes the energizing circuit for the filaments as above described. The switch TS furnishes ground for the energization ofrelays 33, 4 and 30. Relay 33 at its left-hand armature closes circuit for battery 37 to the plate of the amplifier 16, and the inner right-hand armature connects this battery to the plate of the oscillator 15. At its outer right-hand contact it connects the condenser 19 in shunt to the condenser 18 so that oscillations of the lower tone frequency are continuously produced. Relay 4 at its back contacts severs the talking circuit 3 from the radio link and at its front contacts associates the am lifier 16 with the radio transmitting link. ela 30 cuts off the radio incoming channel of te system from call receiving circuits.

If the modulated tele raph signals are to be transmitted from the common-sending and receiving station the switch S is opened and the key T is actuated in accordance with the telegraphic code to open and close the connection from the am lifier 16 to the.outgoing radio transmitting link. If the telegraph signals are to be transmitted from the station at which the operators position OP is located or from an adjacent point the key T is used. This key controls a simlex circuit over the two sides of the link Land thru the windingof relay 31, causing this relay to open and close its armature contacts. When the switch S is openedthe actuation of the armature of relay 31 controls the transmission of signals in the same way as does the key T The tone modulations supplied to the repeatin coil 5 are transmitted to the radio transmitter RT and from there to the distant station in the same manner as that described of the calling tone signals. They may be received by the o erator at the distant station by means 0 the usual head receiver R or any other suitable type of receiver, and for purposes of illustration the receiver R is shown arranged to be plugged into the jack J, in the output side of the first stage amplifier A or in the jack J in the output side of the amplifier 4 if it isdesired to supply two stages of low frequency amplification or into the jack 1 if the signa s are tore'ceived over the link LL, connection being assumed to exist at the point 2.

Since the currents employed for modulated telegraph transmission have only one of the two-tone frequencies utilized for ringing, these telegraph currents will affect only one of the windings of the relay 26 in the receiving station. If the armature of this relay is in one of its extreme positions the efiect of the telegraph current will be to hold the armature in that position, or if it is in the alternate position it will be thrown to'the opposite position and held there. In

either case the circuit of relay 27 will not be opened to cause its release and the signal 29 will not be operated.

It will be understood that various changes may be made in the specific circuits that have been shown for purposes of illustrating the invention within the scope of the appended claims.

What is claimed is:

1. In a wave signaling system, a source of sustained waves of high frequency and a source of waves of lower frequency, means to control the higher frequency waves by the lower to produce modulated telegraph waves and alternative means for utilizing said source of lower frequency waves to transmit a characteristic call signal wave different from the modulated telegraph signal wave.

2. In a selective signaling system, an oscillation generator having control circui s for determining the frequency of the wave generated, meansto make one of said control circuits operative to produce a wave of the corresponding frequency to denote one kind of signal, and means to make said control circuit and a different control circuit alternately operative to produce alternately a wave of said frequency and a wave of a different frequency to denote another kind of si al.

3. n a wave signaling system, means to produce and transmit sustained waves, means to control said waves including an oscillator arranged to oscillate alternately at two frequencies to produce a selective calling signal, and a telegraph key arranged to control said oscillator to oscillate continuouslyfat one of said frequencies to transmit telegraph signals.

4. In a wave signaling system, means to produce and transmit sustained waves, a source of waves for modulating said sus tained waves, a call si nal device at a distant point, a call signa ing key arranged to control said source to generate alternately two modulating waves of different frequency for selectively actuating said call signal device, and telegraph control circuits arranged to control said source to produce a wave of a single modulating frequency for transmitting modulated wave telegraph signals,

5. In a wave signaling system, stations, a

call signal device and a telegraph receiver at one station, a carrler wave modulating system and a source of modulating waves at another station, means to control said source to generate a complex modulating wave for producing a modulated wave for transmission between said stations to actuate selectively said call signal device, and means to control said source to generate a simple wave of a character different from that required to actuate said signal device and to utilize said simple wave for modulated wave telegraphy between said stations.

6. In a wave signaling system, a sending and a receiving station, means to send between said stations a sustained wave modulated by speech waves or by telephone call signals or by telegraph modulating waves, the three kinds. of modulating waves lying within the same low frequency range, a call signal device at the receiving station, a common source of modulating waves for the telephone'call signals and the telegraph signals, control circuits for causing said source to produce modulating waves of a character to actuate selectively said call 'signal device, and other circuits for controlling said source to produce modulating waves for modulated wave-telegraph transmission of a character different fromthat required to actuate said call signal device.

7 In a wave signaling system, means to produce sustained waves and to modulating said waves by signals to be sent, a source of modulating waves comprising an oscillation generator having a plurality of resonant circuit branches for determining the frequency of the oscillations generated, means to make said branches operative in succession to cause the generation of waves of sucessively different frequency to indicate a characteristic calling signal, and means to cause said oscillation generator to produce a wave of constant frequency and to utilize said last-mentioned wave to trans mit modulated wave telegraph signals.

In witness whereof, I hereunto subscribe my name thisil3 da of J ulv, A. D. 1922.

' FR DERICK R. LACK.

In witness whereof, I hereunto subscribe my name this 6th day of September, A. D.

- PAUL B. MURPHY. 

